| Telescopes were invented by accident in 1608 when | | | | special low-light features that allow you to see in near |
| Hans Lippershey, an eyeglass maker in Holland, looked | | | | total darkness; these are great for watching night |
| at a church steeple through two lenses. The discovery, | | | | creatures in their natural habitat. |
| now called the science of optics, caught on | | | | Additional telescope components: |
| immediately and, by 1610, Galileo was tracking the | | | | Since the Earth rotates under the heavens, special |
| moons orbiting Jupiter, giving birth to modern | | | | motors are used so the telescope moves exactly |
| astronomy. Today, sophisticated professional | | | | opposite the Earth's rotation, keeping the objects |
| telescopes search the farthest reaches of the | | | | you're viewing stationary. Obviously, these are |
| universe, but amateur astronomers are having great | | | | necessary only for night viewing. Some telescope |
| fun (and occasionally, making great discoveries) as | | | | packages include these motor mounts; they are |
| they enjoy the beauty of outer space and the Earth. | | | | optional with others. Decide before you buy whether |
| Telescope buying tips: | | | | you'll be day-viewing or night-viewing and buy |
| There are two basic types -- refracting telescopes | | | | accordingly. This motor system is called an equatorial |
| and reflecting telescopes. Both have strengths and | | | | mount; these mounts may include a computer control |
| weaknesses, but each is well-suited to certain | | | | preprogrammed with the 'declination' (rise above the |
| applications. Before you buy, understanding how each | | | | equator) and the 'right ascension' (the object's position |
| type works will help you get the right scope. | | | | relative to other stars). Once these factors are set, the |
| The refractor is Lippershey's original telescope model. | | | | telescope can automatically find and track almost any |
| Simply, it is two or more lenses that focus light, making | | | | celestial object. |
| objects appear closer than they are. Refractors use | | | | Many larger telescopes have a small scope |
| two types of lenses: Convex lenses (like the lens in the | | | | piggy-backed on the side; used to point a scope to the |
| human eye) curve outward, making images appear | | | | general area you are trying to view. These |
| larger. Unlike the eye, they also make objects unclear. | | | | accessories are called finderscopes or spotting |
| Concave lenses curve inward, making images clearer, | | | | scopes. |
| but smaller. Refracting telescopes use combinations of | | | | Telescope care: |
| convex and concave lenses to make images larger | | | | Store your telescope is a cool, dry place. |
| and clearer. Refractors have one basic limitation--they | | | | A well-padded case or footlocker is a great idea, |
| bend light through glass and, since different colors bend | | | | especially if you have a lot of optional paraphernalia. |
| differently, image colors can sometimes be distorted. | | | | When you take it out, let the equipment adjust to the |
| The reflector was invented by Sir Isaac Newton in | | | | air temperature before using it. |
| 1668; it uses mirrors to collect and magnify light. One | | | | Clean the dust off regularly, but carefully. |
| large, bowl-shaped mirror gathers light like a bucket fills | | | | Telescopes are not do-it-yourself items; service and |
| with water then a second mirror reflects it into the | | | | repair shouldn't be needed often but, when it is, take it |
| eyepiece, much the way a curved pipeline changes | | | | to a trained technician. You can probably find one at |
| the direction of flowing water. Since reflecting | | | | your local toy or hobby store. |
| telescopes don't bend light, color isn't distorted. | | | | Telescope terms: |
| However, the inner and outer edges of the mirror may | | | | Modern telescopes are measured in millimeters, sizes |
| have slightly different focal points, so pushing all the | | | | listed as two numbers: 500x100, for example. The first |
| light to the same point sometimes causes 'coma,' a little | | | | is the focal length (distance between the objective lens |
| halo around objects at the edge of the viewing area. | | | | or objective mirror and the eyepiece); the second is |
| The big lens or mirror is called the objective lens or | | | | the aperture (diameter of the objective lens or |
| objective mirror; it determines how much light is | | | | objective mirror). Aperture determines how much light |
| gathered. This is just as important as magnification, | | | | is gathered. To avoid a lot of unnecessary math, the |
| since magnifying something a million times does no | | | | easy rule is "the bigger, the better." This vast stream |
| good if you can't see any details. A larger objective | | | | of light going into the eye has to be compressed to fit |
| means more light enters the scope. The lens users | | | | through the pupil, down to about 0.5mm in diameter, so |
| look through is called the eyepiece. | | | | a 100mm aperture will magnify images roughly 200 |
| Refractors' basic structure has changed little since | | | | times. |
| Lippershey's day, but reflector telescopes now come | | | | For photographers, focal ratio is also important. Divide |
| in several designs, the most common being: | | | | the aperture into the focal length (100mm/500mm) for |
| - Sir Isaac's original, the Newtonian telescope, has one | | | | a focal length of f/5, the minimum considered 'fast' |
| light-gathering mirror that reflects light onto a mirror that | | | | enough for good photos. |
| reflects it into the eyepiece on the side of the tube. | | | | Which telescope is right for me? |
| - The Schmidt-Cassegrain telescope (or SCT) has | | | | If you're a beginner with limited resources, a Newtonian |
| mirrors at each end of the tube. The objective mirror | | | | is probably the best starter model; they can be very |
| has a small hole in the center, through which light | | | | small and give good viewing for the price. |
| passes to the eyepiece. These two mirrors make the | | | | Monoculars (spyglasses) are an absolute necessity if |
| telescope smaller, lighter and easier to handle. | | | | you plan to hoist the Jolly Roger and sail the Spanish |
| - The Nasmyth telescope mixes both designs; instead | | | | Main. |
| of a hole in the objective mirror, it uses a third mirror to | | | | Refractors are generally considered better for |
| reflect the image to the eyepiece. | | | | Earth-based observations such as bird watching. |
| There are also a few specialty telescope types. | | | | Reflectors are preferred for celestial observation, |
| Because these are most often designed for hand-held | | | | since they can be built with larger objective lenses to |
| use, they tend to be small, low-power scopes: | | | | gather more light than a refractor of the same length. |
| - Single hand-held telescopes are now called | | | | Can I take pictures through my telescope? |
| monoculars (more correct, but not nearly as much fun | | | | Absolutely, camera lenses are built using the same |
| as 'spyglass') to distinguish them from larger, | | | | optics as a refractor, especially telephoto lenses. Many |
| tripod-mounted models. | | | | telescopes either include camera mounts or have |
| - Double telescopes (one for each eye) are binoculars; | | | | them available as optional equipment. The |
| these take full advantage of human's stereoscopic | | | | Schmidt-Cassegrain model is generally preferred by |
| vision. | | | | serious astro-photographers. |
| - Night vision scopes are monoculars or binoculars with | | | | |